Welding wire preheating system and method

ABSTRACT

In a welding system, a preheating process is carried out prior to initiation of a welding arc, such as upon depression of a trigger or switch on a welding torch. The preheating process involves generation and application of desired currents and voltages to a welding electrode from a power supply. Preheating is continued until the welding electrode reaches a desired temperature or resistance, which may be determined by reference to an increasing voltage, a decreasing current, a peaked and declining voltage, resistance and/or power measurements, and so forth. Following preheating, a desired welding process may begin with initiation of the welding arc.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Non-Provisional Patent Application of U.S.Provisional Patent Application No. 61/761,007, entitled “Welding WirePreheating System and Method”, filed Feb. 5, 2013, which is hereinincorporated by reference in its entirety for all purposes.

BACKGROUND

The invention relates generally to welders, and more particularly to awelder configured to perform a preheating operation on welding wireprior to execution of a weld.

A wide range of welding systems and welding control regimes have beenimplemented for various purposes. In continuous welding operations,metal inert gas (MIG) techniques allow for formation of a continuingweld bead by feeding welding wire shielded by inert gas from a weldingtorch. Electrical power is applied to the welding wire and a circuit iscompleted through the workpiece to sustain an arc that melts the wireand the workpiece to form the desired weld.

Advanced forms of MIG welding are based upon generation of pulsed powerin the welding power supply. That is, various pulsed regimes may becarried out in which current and/or voltage pulses are commanded by thepower supply control circuitry to regulate the formation and depositionof metal droplets from the welding wire, to sustain a desired heatingand cooling profile of the weld pool, to control shorting between thewire and the weld pool, and so forth. However other welding regimesexist and are commonly used that provide power that is not pulsed. Thevarious regimes may rely on “electrode positive” or “electrode negative”polarities, and the present disclosure may relate to any and all ofthese.

While very effective in many applications, MIG welding techniques mayexperience different initial welding performance based upon whether theweld is started with the electrode “cold” or “hot”. In general, a coldelectrode start may be considered a start in which the electrode tip andadjacent metals are at or relatively near the ambient temperature. Hotelectrode starts, by contrast, are typically those in which theelectrode tip and adjacent metals are much more elevated, but below themelting point of the electrode wire. In some applications, it isbelieved that initiation of arcs and welds is facilitated when theelectrode is hot. However, the current state of the art does not provideregimes designed to ensure that the electrode is heated prior toinitiate of welds.

There is a need, therefore, for improved welding strategies that allowfor welding initiation with a heated electrode so as to improve weldperformance.

BRIEF DESCRIPTION

The present disclosure relates to methods and systems designed torespond to such needs. In accordance with certain aspects, a weldingmethod comprises receiving a signal indicative of initiation of weldingprocess, and prior to initiating a welding arc, controlling voltage orcurrent applied to a welding electrode to preheat the electrode.Feedback voltage and current are monitored to determine a termination ofpreheating, and then preheating is terminated and the welding arc isinitiated in accordance with a desired welding protocol.

In accordance with another aspect, a welding method comprises receivinga signal indicative of initiation of welding process, and, prior toinitiating a welding arc, automatically controlling voltage or currentapplied to a welding electrode to preheat the electrode. Preheating isthen terminated when the electrode reaches a desired resistance or adesired power level as determined based upon monitored current andvoltage applied to the welding electrode, and the welding arc isinitiated in accordance with a desired welding protocol.

In accordance with a further aspect, a welding system, comprises a powersupply comprising power conversion circuitry and control circuitryconfigured to cooperate to provide welding current and voltage to awelding electrode, a signal source configured to provide a signal forinitiation of a welding process, and current and voltage monitoringsensors. The control circuitry is configured to, prior to initiating awelding arc, control voltage and current applied to a welding electrodeto preheat the electrode, to monitor the applied voltage and current todetermine a termination of preheating, and to terminate preheating andinitiate the welding arc in accordance with a desired welding protocol.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical representation of an exemplary MIG weldingsystem illustrating a power supply coupled to a wire feeder forperforming welding operations in which an electrode is heated prior toweld initiation;

FIG. 2 is a diagrammatical representation of exemplary control circuitrycomponents for a welding power supply of the type shown in FIG. 1;

FIG. 3 is a flow chart illustrating exemplary steps in a welding processin which the electrode is preheated; and

FIGS. 4 and 5 are illustrating voltage and current waveforms generatedand applied for preheating an electrode.

DETAILED DESCRIPTION

Turning now to the drawings, and referring first to FIG. 1, an exemplarywelding system is illustrated as including a power supply 10 and a wirefeeder 12 coupled to one another via conductors or conduits 14. In theillustrated embodiment the power supply 10 is separate from the wirefeeder 12, such that the wire feeder may be positioned at some distancefrom the power supply near a welding location, and the conduits 14 areembodied as a welding cable that transmits control signals and powerbetween the power supply 10 and the wire feeder 12. However, it shouldbe understood that the wire feeder, in some implementations, may beintegral with the power supply. In such cases, the conduits 14 would beinternal to the system. In embodiments in which the wire feeder isseparate from the power supply, terminals are typically provided on thepower supply and on the wire feeder to allow the conductors or conduitsto be coupled to the systems so as to allow for power and gas to beprovided to the wire feeder from the power supply, and to allow data tobe exchanged between the two devices.

The system is designed to provide wire, power and shielding gas to awelding torch 16. As will be appreciated by those skilled in the art,the welding torch may be of many different types, and typically allowsfor the feed of a welding wire and gas to a location adjacent to aworkpiece 18 where a weld is to be formed to join two or more pieces ofmetal. A second conductor is typically run to the welding workpiece soas to complete an electrical circuit between the power supply and theworkpiece.

The system is designed to allow for data settings to be selected by theoperator, particularly via an operator interface 20 provided on thepower supply. The operator interface will typically be incorporated intoa front faceplate of the power supply, and may allow for selection ofsettings such as the weld process, the type of wire to be used, voltageand current settings, and so forth. In particular, the system isdesigned to allow for MIG welding with various steels, aluminums, orother welding wire that is channeled through the torch. These weldsettings are communicated to control circuitry 22 within the powersupply.

The control circuitry, described in greater detail below, operates tocontrol generation of welding power output that is applied to thewelding wire for carrying out the desired welding operation. In certainpresently contemplated embodiments, for example, the control circuitrymay be adapted to regulate the MIG welding regime, while also providingpower for preheating the welding wire electrode prior to initiation ofthe weld. As described more fully below, such heating may be controlledby altering operating parameters of current and voltage applied to theelectrode through the welding cable and torch.

The control circuitry is thus coupled to power conversion circuitry 24.This power conversion circuitry is adapted to create the output power,such as pulsed and non-pulsed waveforms that will ultimately be appliedto the welding wire at the torch. Various power conversion circuits maybe employed, including choppers, boost circuitry, buck circuitry,inverters, converters, and so forth. The configuration of such circuitrymay be of types generally known in the art in and of itself. The powerconversion circuitry 24 is coupled to a source of electrical power asindicated by arrow 26. The power applied to the power conversioncircuitry 24 may originate in the power grid, although other sources ofpower may also be used, such as power generated by an engine-drivengenerator, batteries, fuel cells or other alternative sources. Finally,the power supply illustrated in FIG. 1 includes interface circuitry 28designed to allow the control circuitry 22 to exchange signals with thewire feeder 12.

The wire feeder 12 includes complimentary interface circuitry 30 that iscoupled to the interface circuitry 28. In some embodiments, multi-pininterfaces may be provided on both components and a multi-conductorcable run between the interface circuitry to allow for such informationas wire feed speeds, processes, selected currents, voltages or powerlevels, and so forth to be set on either the power supply 10, the wirefeeder 12, or both.

The wire feeder 12 also includes control circuitry 32 coupled to theinterface circuitry 30. As described more fully below, the controlcircuitry 32 allows for wire feed speeds to be controlled in accordancewith operator selections, and permits these settings to be fed back tothe power supply via the interface circuitry. The control circuitry 32is coupled to an operator interface 34 on the wire feeder that allowsselection of one or more welding parameters, particularly wire feedspeed. The operator interface may also allow for selection of such weldparameters as the process, the type of wire utilized, current, voltageor power settings, and so forth. The control circuitry 32 is alsocoupled to gas control valving 36 which regulates the flow of shieldinggas to the torch. In general, such gas is provided at the time ofwelding, and may be turned on immediately preceding the weld and for ashort time following the weld. The gas applied to the gas controlvalving 36 is typically provided in the form of pressurized bottles, asrepresented by reference numeral 38.

The wire feeder 12 includes components for feeding wire to the weldingtorch and thereby to the welding application, under the control ofcontrol circuitry 36. For example, one or more spools of welding wire 40are housed in the wire feeder. Welding wire 42 is unspooled from thespools and is progressively fed to the torch. The spool may beassociated with a clutch 44 that disengages the spool when wire is to befed to the torch. The clutch may also be regulated to maintain a minimumfriction level to avoid free spinning of the spool. A feed motor 46 isprovided that engages with feed rollers 48 to push wire from the wirefeeder towards the torch. In practice, one of the rollers 48 ismechanically coupled to the motor and is rotated by the motor to drivethe wire from the wire feeder, while the mating roller is biased towardsthe wire to maintain good contact between the two rollers and the wire.Some systems may include multiple rollers of this type. Finally, atachometer 50 may be provided for detecting the speed of the motor 46,the rollers 48, or any other associated component so as to provide anindication of the actual wire feed speed. Signals from the tachometerare fed back to the control circuitry 36, such as for calibration asdescribed below.

It should be noted that other system arrangements and input schemes mayalso be implemented. For example, the welding wire may be fed from abulk storage container (e.g., a drum) or from one or more spools outsideof the wire feeder. Similarly, the wire may be fed from a “spool gun” inwhich the spool is mounted on or near the welding torch. As notedherein, the wire feed speed settings may be input via the operator input34 on the wire feeder or on the operator interface 20 of the powersupply, or both. In systems having wire feed speed adjustments on thewelding torch, this may be the input used for the setting.

Power from the power supply 10 is applied to the wire, typically bymeans of the welding cable 14 to a torch cable 52 to a work cable 53 ina conventional manner. Similarly, shielding gas is fed through the wirefeeder and the torch cable 52. During welding operations, the wire isadvanced through the welding cable jacket towards the torch 16. Withinthe torch 16, an additional pull motor 54 may be provided with anassociated drive roller, particularly for aluminum alloy welding wires.The motor 54 is regulated to provide the desired wire feed speed asdescribed more fully below. A trigger switch 56 on the torch provides asignal that is fed back to the wire feeder 12 and therefrom back to thepower supply 10 to enable the welding process to be started and stoppedby the operator. That is, upon depression of the trigger switch, gasflow is begun, wire is advanced, power is applied to the torch cable 52and through the torch 16 to the advancing welding wire. These processesare also described in greater detail below. Finally, the work cable 53and associated clamp 58 allow for closing an electrical circuit from thepower supply 10 through the welding torch 16, the electrode (wire), andthe workpiece 18 for maintaining the welding arc during operation.

It should be noted throughout the present discussion that while the wirefeed speed may be “set” by the operator, the actual speed commanded bythe control circuitry will typically vary during welding for manyreasons. For example, automated algorithms for “run in” (initial feed ofwire for arc initiation) may use speeds derived from the set speed.Similarly, various ramped increases and decreases in wire feed speed maybe commanded during welding. Other welding processes may call for“cratering” phases in which wire feed speed is altered to filldepressions following a weld. Still further, in pulsed welding regimes,the wire feed speed may be altered periodically or cyclically.

FIG. 2 illustrates an exemplary embodiment for the control circuitry 22designed to function in a system of the type illustrated in FIG. 1. Theoverall circuitry, designated here by reference numeral 60, includes theoperator interface 20 discussed above and interface circuitry 28 forcommunication of parameters to and from downstream components such as awirefeeder, a welding torch, and various sensors and/or actuators. Thecircuitry includes processing circuitry 62 which itself may comprise oneor more application-specific or general purpose processors, designed tocarry out welding regimes, make computations for waveforms implementedin welding regimes, and so forth. The processing circuitry is associatedwith driver circuitry 64 which converts control signals from theprocessing to drive signals that are applied to power electronicswitches of the power conversion circuitry 24. In general, the drivercircuitry reacts to such control signals from the processing circuitryto allow the power conversion circuitry to generate controlled waveformsfor welding regimes. The processing circuitry 62 will also be associatedwith memory circuitry 66 which may consist of one or more types ofpermanent and temporary data storage, such as for providing the weldingregimes implemented, storing welding parameters, storing weld settings,storing error logs, and so forth.

As discussed above, the present electrode preheating techniques allowfor a preheating regime to be implemented, when desired, with anywelding program carried out by the system. In the embodiment illustratedin FIG. 2, the scheme is implemented by separate programmed protocolsimplemented by the processing circuitry 62. That is, a welding regimeprotocol may comprise any known or future developed welding program,such as pulsed and non-pulsed regimes, as indicted by reference numeral68. A preheating protocol is provided that may always be used, or thatmay be used only when selected by an operator, as indicated by referencenumeral 70. In practice, the preheating protocol may be implemented and,upon termination, control may be taken in accordance with the selectedwelding protocol The waveforms generated based upon these protocols mayresult from software only, hardware, and/or firmware that is implementedby the processing circuitry and/or that forms part of the control anddriver circuitry illustrated. The preheating protocol and the weldingprotocol will generally make use of feedback from sensors and inputs.These inputs may include weld settings, pre-programmed logic, and inputsfrom sensors 72 received during the welding process. Sensed parameterswill typically include, for example, current and voltage applied to thewelding torch, and therethrough, to the welding electrode.

FIG. 3 illustrates exemplary logic for implementation of the preheatingand welding techniques. In a typical process, the welding operator willmake certain selections to define the welding setup, as indicatedgenerally by reference numeral 74. Such selections may include a weldingprocess, voltages, currents, wire feed speeds, and so forth. Theselections may be made on the power supply, on the wire feeder, or both.At step 76, where desired, the operator may select to perform thepreheating procedure described in the present disclosure. In certainsystems, the preheating procedure may be automatically performed,although it is presently contemplated that the operator may select orde-select the preheating. Moreover, while manual welding systems aredescribed, the same preheating processes may be performed in automated(e.g., robotic) systems.

At step 78, with the workpieces, cable, and other system componentsready to execute the desired welds, the operator may either touch thewire electrode onto the workpiece, or proceed with a non-touch start. Ina non-touch start, the electrode will be spaced from the workpiece. Atstep 80, then, the operator may pull the trigger on the torch toinitiate the weld in a conventional manner. However, rather initiate thearc as is normally done for weld initiation, where the preheat sequenceis to be performed, preheating will be performed as indicated at step82. As described below, several scenarios may be envisaged forpreheating, in general, however, the voltage and current are controlledfor a sufficient period to raise the temperature of the weld electrodeto a particular point. As indicated at step 84, the logic may cycleduring this preheating phase, with the system determining whether thetermination point of the preheating (see below) has been reached asindicated at step 84. If not, the preheating protocol is followed untilthe termination point is reached. Thereafter, the arc may be initiatedas indicated at step 86 and the selected welding regime protocol will befollowed starting with the preheated electrode.

Slightly different logic may be employed depending upon whether thestart of the weld is from the touching situation or non-touch. Forexample, when performing a touching start, the system may implement aslight delay to detect the touch prior to preheating. In certainembodiments, prior to initiation of a welding arc, an amount of timethat the electrode has not been under an arc condition may bedetermined, at least one of a preheating time, current, or voltage maybe determined based on the determined amount of time, and termination ofthe preheating cycle may be terminated based on a timer (e.g.,predetermined amount of time) that is set based on the determinedpreheating time, current, or voltage, for example. Moreover, the logicfor implementing the preheating protocol may, in some cases, altersomewhat the welding regime that follows immediately after preheating.That is, because the electrode will be preheated, a lower initialcurrent may be employed in the subsequent welding process. In presentlycontemplated embodiments, time periods while preheating may vary,depending upon such factors as the wire used, the currents and voltagesapplied, and so forth. Typical periods for preheating may vary, forexample, between 10 and 20 ms. In practice, a baseline voltages andamperages may be set for different wire sizes, such as by establishing abaseline at approximately 100 A, with voltages set based upon the wiretype and size. The wire type and size, as well as the wire feed speedused during welding and any different wire feed speeds used during arun-in phase that will typically be selected by the operator during thewelding setup discussed above.

In general, the preheating may be thought of as adding energy to theelectrode during what is effectively a short circuit between theelectrode and the workpiece. As will be appreciated by those skilled inthe art, the resistance of the electrode will typically increase as itis heated, and this increase in resistance may form the basis for thepreheating protocol as well as for the point of termination ofpreheating. By monitoring voltage and current, then, and controllingthese parameters the process may be free from dependency upon specifictiming. In certain contemplated embodiments, the preheating protocol isbased upon application of a fixed current (such as based on the wireselected) and increasing voltage from an initial level to a terminationlevel when a voltage threshold is reached. Because the resistance of thewire (indicating a rising temperature) is indicated from the increasingvoltage, with the current held steady, in accordance with Ohm's law, theprotocol allows for raising the electrode resistance (and hence thetemperature of th wire) to a desired and consistent level by simplymonitoring the applied voltage. By way of example, a voltage level of 8vmay be used as a threshold with a constant current of approximately 200A. Once the voltage threshold is met, then, the system switches to thearc start phase, but which may be initiated at a lower or morepredictable current than it would have been with a cold electrode orwith an electrode of different, unknown, temperatures.

FIG. 4 graphically illustrates waveforms in accordance with this aspectof the process. The graphically representation 88 is here presented withvoltage along a vertical axis 90, current along a vertical axis 92, andtime along a horizontal axis 94. A current waveform 96 can be seen aswell as a voltage waveform 98. As noted above, at a point of initiationof the process, indicated generally by reference numeral 100, thecurrent and voltage are applied by the power supply to the torch andthen through to the welding electrode. In this example, the current isincreased to a generally constant level as indicated by referencenumeral 102, in this case approximately 100 A. At the same point ofinitiation, the voltage is increased to an initial voltage ofapproximately 1.4v, and is increased gradually to a level ofapproximately 2.5v. In this example the current and voltage are direct,and continuous. The point of termination at approximately 2.5v,corresponds to a point where it has been determined that the electrodehas been sufficiently heated to begin welding. At that point, thecurrent is reduced as indicated at reference numeral 104 as is thevoltage as indicated at reference numeral 108. Thereafter, although notshown in FIG. 4, the welding process may begin with initiation of thearc.

FIG. 5 illustrates an alternative control scheme as indicated generallyby reference numeral 110. Here again, voltage is illustrated along avertical axis 90 with current along a vertical axis 92, and time along ahorizontal axis 94. In this case, both the current and voltage areapplied to initiate the process, in this case a current of approximately200A is applied. The voltage is applied at an initial level andincreases until the wire reaches a maximum temperature and flattens outor declines, as indicated generally by reference numerals 112 and 114.This decline may indicate that the wire will not undergo furtherresistance change by the application of additional energy. Thus, bymonitoring the applied voltage, the trigger for terminating the processmay be determined, followed by application of the selected weldingprotocol.

Still further variations may include, for example, ramping up current,such as to reduce the time for preheating. In a further alternative,rather than using a voltage threshold, a change in ramp rate of thevoltage may indicated that the wire is at a maximum current density.Still further, the protocol may employ a constant voltage and watch fora drop in current to a threshold or a change in current ramp rate. Aswill be appreciated by those skilled in the art, or into therelationships dictated by Ohm's law, these various determinations willtypically correspond to an increase in resistance of the weldingelectrode due to heating, which may be terminated at a desired voltage,current, power or any other desired threshold. With this in mind, it mayalso be possible to measure power and/or resistance and terminate thepreheating processing based upon such analysis. The power and/orresistance may be determined, for example, based upon the applied ordetected voltages and currents. It should be noted that, while referencemay be made in the current disclosure to controlling and/or monitoringvoltage and current (or power, resistance, etc.), this should beunderstood to mean that one or both current and voltage may becontrolled, and the other monitored. In fact, it is considered that“controlling” one of the parameters (e.g., voltage) includes monitoringinsomuch as the process of controlling will include knowing the value,whether through active control, feedback, or both.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A welding method, comprising: receiving a signal indicative ofinitiation of welding process; prior to initiating a welding arc,controlling voltage or current applied to a welding electrode to preheatthe electrode; monitoring feedback voltage and current to determine atermination of preheating; and terminating preheating and initiating thewelding arc in accordance with a desired welding protocol.
 2. The methodof claim 1, wherein the signal is received from a welding torch as aresult of an operator depressing a trigger of the torch.
 3. The methodof claim 1, wherein during preheating, current applied to the weldingelectrode is maintained generally constant and voltage feedback from theelectrode is monitored for an increase.
 4. The method of claim 3,wherein preheating is terminated when the voltage feedback from theelectrode reaches a predetermined threshold value.
 5. The method ofclaim 3, wherein preheating is terminated when the voltage feedbackreaches a peak and declines.
 6. The method of claim 1, wherein duringpreheating, voltage applied to the welding electrode is maintainedgenerally constant and current feedback from the electrode is monitoredfor a decrease.
 7. The method of claim 1, wherein the applied voltageand current are monitored to determine when the welding electrode hasreached a desired resistance, and preheating is then terminated.
 8. Themethod of claim 1, wherein the applied voltage and current are monitoredto determine when the welding electrode has reached a desired powerlevel, and preheating is then terminated.
 9. The method of claim 1,wherein at least one of the applied current, the applied voltage and thetermination of preheating is based upon a type and size of theelectrode.
 10. A welding method, comprising: receiving a signalindicative of initiation of welding process; prior to initiating awelding arc, automatically controlling voltage or current applied to awelding electrode to preheat the electrode; terminating preheating whenthe electrode reaches a desired resistance or a desired power level asdetermined based upon monitored current and voltage applied to thewelding electrode; and initiating the welding arc in accordance with adesired welding protocol.
 11. The method of claim 10, whereintermination of preheating is based upon a feedback voltage reaching adesired threshold.
 12. The method of claim 10, wherein termination ofpreheating is based upon a feedback current reaching a desiredthreshold.
 13. The method of claim 10, wherein termination of preheatingis based upon a feedback voltage reaching maximum level and declining.14. The method of claim 10, wherein at least one of the applied current,the applied voltage and the termination of preheating is based upon atype and size of the electrode.
 15. A welding system, comprising: apower supply comprising power conversion circuitry and control circuitryconfigured to cooperate to provide welding current and voltage to awelding electrode; a signal source configured to provide a signal forinitiation of a welding process; and current and voltage monitoringsensors; wherein the control circuitry is configured to, prior toinitiating a welding arc, control voltage and current applied to awelding electrode to preheat the electrode, to monitor the appliedvoltage and current to determine a termination of preheating, and toterminate preheating and initiate the welding arc in accordance with adesired welding protocol.
 16. The system of claim 15, wherein the signalsource comprises a welding torch.
 17. The system of claim 15, whereinduring preheating, current applied to the welding electrode ismaintained generally constant and voltage feedback is monitored for anincrease.
 18. The system of claim 17, wherein preheating is terminatedwhen the voltage applied to the electrode reaches a predeterminedthreshold value.
 19. The system of claim 17, wherein preheating isterminated when the applied voltage reaches a peak and declines.
 20. Thesystem of claim 15, wherein during preheating, voltage applied to thewelding electrode is maintained generally constant and current ismonitored for a decrease.
 21. The system of claim 15, wherein theapplied voltage and current are monitored to determine when the weldingelectrode has reached a desired resistance, and preheating is thenterminated.
 22. The system of claim 15, wherein the applied voltage andcurrent are monitored to determine when the welding electrode hasreached a desired power level, and preheating is then terminated.
 23. Awelding method, comprising: receiving a signal indicative of initiationof welding process; prior to initiating a welding arc, determining anamount of time that a welding wire has not been under an arc condition;determining at least one of a preheating time, current, or voltage basedon the determined amount of time; terminating a preheat cycle based on atimer; and initiating the welding arc in accordance with a desiredwelding protocol.